1. Field of the Invention
The present invention relates to disposable absorbent products such as disposable diapers, sanitary napkins and incontinence pads. More specifically, it relates to absorbent products exhibiting excellent permeability and diffusibility of the absorbed liquid in the absorbent layer without leakage, thereby providing good dryness and comfort to the user.
2. Description of the Prior Art
Hitherto, various proposals have been advocated for absorbent products' properties aimed at improving the absorption rate of urine or blood, improving the dryness after absorption, or reducing leakage.
Most of such proposals relate to improvement of the liquid permeable surface sheet or surface nonwoven fabric (as disclosed in the official gazette notice for JP-A-58-60068, the official gazette notice for JP-A-1-148879 and the official gazette notice for JP-A-2-169774), use of water-absorbent resins having a specific performance or property, disposition of an absorbent resin in the absorbent layer, use of a hydrophilic diffusion layer comprising a nonwoven fabric or a water-absorbent paper, and an embossing method for the absorbent layer. Thus few improvements concerning the absorbent layer itself containing an absorbent resin have been proposed so far. This is because conventional disposable diapers have an absorbent layer made of materials with a high hydrophilic property, such as fluff pulp, water absorbent paper and water absorbent resin.
These days, with the property improvement of absorbent products such as disposable diapers and sanitary napkins, such products tend to be used over a long time. Further, as to disposable diapers, as they become thinner, the ratio of water absorbent resin/fiber substrate therein tends to become greater. On the other hand, satisfactory shape retention or unity of the water absorbent resin/fiber substrate can not be obtained with an absorbent layer comprising a water-absorbent resin and a conventional cellulose fiber such as fluff pulp and water absorbent paper, regardless of the application of the water-absorbent resin, namely, whether in a method of sandwiching between pulp layers or water absorbent papers, or in a method of mixing with pulp. That is, hydrophilic cellulose fibers that absorb and retain liquid such as urine and blood by physical capillary action have problems such as susceptibility to deformation by an external force such as the wearer's movement during a period of water absorption or after water absorption to ruin the unity of the water absorbent resin/fiber substrate, which lead to leakage and deterioration of dryness.
Proposals to prevent deformation of absorbent layers in the wet state, that is, to provide resilience to enable restoration of the absorbent layer when an external force such as compression and distortion is applied thereto, have been made. For example, an attempt has been made to form an absorbent layer by sandwiching a water absorbent resin between sheets comprising a synthetic fiber. Although this method can improve shape retention in the wet state to some degree, it causes a problem in that when the amount of the water absorbent resin is sufficiently large, the water absorbent resin sandwiched between the fiber sheets forms a gel layer after absorption, and the gel layer can be displaced by an extenal force to ruin the unity between the water absorbent resin gel/fiber substrate and cause leakage. Further, since synthetic fibers are not hydrophilic, a problem or deterioration of the permeability and the diffusibility of the liquid occurs.
Moreover, a proposal has been made to improve shape retention of the absorbent layer by mixing and dispersing water-absorbent resin in a fiber substrate which is a combination of a heat-adhesive synthetic fiber and fluff pulp with heat treatment. However, although this method provides improvement of shape retention, since the hydrophilic property of the absorbent layer deteriorates as the ratio of the synthetic fiber increases, a problem of deterioration of the liquid's permeability or diffusibility occurs as compared with a conventional absorbent layer consisting of cellulose fiber.